Well,
Rex Allen, Wild Bill Elliott, Gene Autry (as allowed), and Buck Jones series are all complete. Roy Rogers books are not in the public domain and I have no clue as to the Cisco Kid. Its not becoming available in the public domain, the books that are here have long been in the PD, (actually, nothing will probably enter PD in the US again), it is just having people willing to purchase these character driven western and scan them and edit them. Many are hard to find.
Hope that helps a little.
movielover